Apparatus for introducing gas into a liquid

ABSTRACT

An apparatus for introducing gas, e.g. atmospheric oxygen, into a liquid such as waste water or sewage comprises a plurality of ribs of airfoil cross-section and forming venturi nozzles which are first constricted and then widened in the direction of liquid flow. The ribs are formed with minute passages for introducing the gas into the liquid perpendicular to the direction of liquid flow across the ribs.

FIELD OF THE INVENTION

The present invention relates to an apparatus or device for introducinga gas into a liquid and, more particularly, to an apparatus for treatinga liquid with the gas, e.g. to dissolve the gas or a component thereofinto the liquid.

BACKGROUND OF THE INVENTION

Apparatus for treating a liquid with the gas can have many utilities andof particularly great interest at the present time are systems fordissolving oxygen in liquids such as waste water as part of apurification thereof.

Waste-water purification systems may involve the aerobic decompositionof organic components of waste water, e.g. in an activated sludge tank,with the result that a purified decantate can be removed free from toxicor noxious components. Of course, it is also interesting to introduceother gases, such as carbon dioxide, into water for various purposes, todissolve ammonia in water and, in general, treat a liquid phase with gasphase.

A wide variety of techniques have been developed for this purposeranging from the simple injection of the gas into a stationary body ofwater through so-called aeration stones, spraying the liquid into thegas, rapidly mixing liquid in such a manner as to draw gas into it, etc.

A particularly advantageous approach has been described in the Germanpublished application (Offenlegungschrift) DT-OS 2,223,460 in which theliquid is pumped through a multiplicity of passages into which capillaryribs open to introduce the gas. The result is a highly efficient gasdiffusion system in which the liquid streams passing through thechannels entrain the gas in the form of small bubbles. The bubble sizedepends upon the velocity of the liquid stream flowing across thelateral opening of the capillary into the flow passage because thebubble is formed by a chearing at this opening.

When such a system is used for waste waters and othercontaminant-containing liquid streams, the flow passages are readilyblocked or obstructed and the necessary high velocities cannot beobtained.

Thus, while the system is highly efficient if satisfactory liquidvelocities and flow rates can simultaneously be attained, it has notbeen found to be practical for many applications.

OBJECTS OF THE INVENTION

It is the principal object of the present invention to provide anapparatus for the mixing of a gas with a liquid which is economical tooperate with respect to energy losses or consumption, is more effectiveas prior-art devices of the aforedescribed type and provides a highlyefficient combination of the gas with the liquid.

Another object of the invention is to provide a system for the purposesdescribed which is less prone to blocking or obstruction than theearlier systems, is particularly suited for the treatment of wastewater, and which is free from other disadvantages characterizinggas-dispersing systems in finely divided form in a liquid phase.

SUMMARY OF THE INVENTION

These objects and others which will become hereinafter apparent areattained, in accordance with the present invention, by providing aplurality of gas-distribution ribs with aerodynamic or airfoil profilesacross which the liquid flows and which are provided along a surface ofthe aerodynamic or streamlined ribs with passage-forming means forfeeding the gas into the liquid generally transversely to its flowdirection. Advantageously, the profiles of adjacent ribs define betweenthem venturi nozzles.

The term "venturi nozzle" is here used to define a passage which isinitially (in the direction of flow of the liquid) converges relativelysharply to a minimum spacing and thereafter widens more slowly.Preferably the gas-discharging means is disposed immediately upstream ofthis last divergence.

A gap between the ribs shaped as a venturi nozzle in the mannerdescribed, with the gas-discharging means disposed ahead of thedivergence, permits the liquid to suck the gas from the gas outletpassages and shear the gas at high velocity in the constriction from thegas flow in the form of especially fine bubbles.

The gas is sucked by the liquid from the passages by the venturi effect.

The gas discharge means can be a perforated plate or a porous body, e.g.an aeration stone made of any convenient material, e.g. sinteredparticles of metal, ceramic or synthetic resin, which is perferablydisposed on an upper or lower surface of the rib. The ribs can beoriented horizontally.

According to a feature of the invention, the ribs are connected with asource of gas, e.g. oxygen or atmospheric air whose oxygen is to bedissolved in waste water by pipes feeding the group of ribs, the ribsbeing hollow to distribute the gas to the several gas-permeable membersforming the discharge means. Alternatively, the ribs can communicatewith a common chamber supply with the gas or may be provided with amanifold which feeds the gas to them.

The bubbles sheared by the high-velocity liquid in the narrowest part ofeach constriction are entrained by the liquid flowing between the ribsand are thereafter dispersed in the remaining body of liquid. Because ofthe relatively low volume of each bubble, the bubbles rapidly dissolve.The divergence at the end of the flow passage between each pair of ribsacts as a diffuser in which velocity is transformed again into pressureafter pressure has been transformed into an increased velocity in thenarrowest part of the constriction thereby minimizing the total energyconsumption of the device.

The displacement of the liquid can be effected by a submerged pumpadapted to drive the liquid through the gaps between the ribs of the gasdistributor. In this case, it is advantageous to provide the gasdistributor in the form of a grid of such ribs of the outlet of a nozzleor duct traversed by the liquid and having the submerged pump at theintake end.

Of course, nozzles can be provided to inject the carrier liquid into thegap between the ribs so that the displacement of the larger body ofliquid is effected in accordance with ejector principles.

According to another feature of the invention, the ribs are formed asannular or ring-shaped members, e.g. as horizontal annular hollow discsat the end of a vertical pipe and are spaced along the axis thereof toprovide radial venturi gaps. The entire assembly can be received in asewage clarification tank and a pump can be provided to circulate wateraxially downwardly through the duct and radially outwardly through theannular ribs.

According to the invention we can make use of a propeller pump and aradial pump whose rotor is disposed within the space surrounded by theannular ribs can also be employed. Thus the water circulation device canbe used to circulate the contents of the tank as well as aerate thelatter.

The pump motor can be disposed above the liquid level, the shaft of thepump extending vertically into the assembly as described.

According to another aspect of the invention, a pump rotor or impellercan be formed from a plurality of radial pump wheels which can alternatewith annular ribs of the type described and furthermore the annular ribsand the radial pump wheels can be rotatable counter to one another, i.e.in opposite senses.

Such an arrangement not only permits a more effective circulation ofliquid downwardly and outwardly through the unit within the clarifiervessel but also increases the relative velocity between the liquid andthe ribs, thereby increasing the shearing effect and reducing thediameter of the gas bubbles which are formed. One or more ribs in any ofthe embodiments described can be provided with one or more vibrators toincrease the relative velocity of the liquid and the ribs. The briefaccelerations imparted by the vibrator to the ribs has been found toproduce especially small bubbles and permits the flow velocity of theliquid to be reduced without detrimentally affecting the overallefficiency of the device.

Especially high relative velocities are obtained when one or more ribsare provided as multiblade propellers cooperating with fixed ribs. Theribs can also be the liquid displacing vanes of a radial pump.

The invention is not only applicable to dissolution of gases in liquidsbut may be used in addition for the separation of liquids and solidparticles by flotation, i.e. systems in which gas bubbles are generatedto adhere to solid particles.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a vertical section through a plurality of horizontallydisposed ribs, drawn to an enlarged scale and illustratingdiagrammatically the principles of the present invention;

FIG. 2 is an axial cross section through an apparatus according to thepresent invention, also diagrammatically represented;

FIG. 3 is a vertical axial cross-sectional view through a gas-dispersingdevice for a waste water treatment plant;

FIG. 4 is a section similar to FIG. 3 through another device for thispurpose, also according to the invention;

FIG. 5 is a view similar to FIG. 3 but illustrating another embodimentof the invention;

FIG. 6 is a section taken along the line VI--VI of FIG. 5; and

FIG. 7 is a vertical section through another embodiment.

SPECIFIC DESCRIPTION

FIG. 1 shows three ribs in schematic cross section forming a grid of agas-dispersing device, e.g. of the type shown in FIG. 2. The ribs 1, 2and 3 are of aerodynamic profile and thus each has a streamlined orrounded upstream end as represented at 1a, 2a, 3a against which theoncoming stream of liquid represented by the arrow L impinges.

The upper and lower surface 1b and 1c, 2b and 2c, 3b and 3c define apair of flow passages represented generally at 1d and 2d respectively.Each of these passages initially converges in a zone a, remains constantover a zone b and diverges over a zone c, the divergence of zone c beingless rigid than the convergence in the zone a. The zone b represents themaximum constriction of the flow passages 1d and 2d. The flow passages1d and 2d thus constitute venturi nozzles which tend to draw gas intothe liquid from the passages in a block 4 disposed along the upper andlower surfaces of each rib substantially over a major portion of thewidth of the zone b. The blocks 4 are composed of sintered metals,ceramic or synthetic resin and are permeable to gas so as to effectivelyhave a multiplicity of capillary passages from which the gas can besucked by the venturi effect. Because of the constricting nature of theventuri nozzle, the liquid has a maximum flow velocity in the zone b.

The upper and lower walls of each rib 1, 2, 3 is provided with seats 1e,2e and 4e in which the gas permeable member 4 is received.

As the gas is torn from the passages of its permeable block 4, it isentrained with a liquid phase and dispersed into surrounding liquid atthe downstream side d of the device. Gas is supplied to the ribs via aline represented diagrammatically at 5. It will be apparent that theribs extend horizontally so that the venturi nozzles are generally flatand horizontal and are not readily obstructed by contaminants containedin the waste water or sewage.

FIG. 2 illustrates a gas-dispersal device particularly adapted toenriching waste water or sewage with oxygen or for treating naturalwater, e.g. drinking water with oxygen by aeration. In this embodiment amultiplicity of ribs 6, generally similar to the ribs 1-3 and operatingin accordance with the same principles, form a grid work 6a at thedownstream side of duct 7 which has intake 7a and an outlet 7b. Betweenthe small-cross section intake 7a and the large-cross section outlet 7b,the duct 7 diverges as represented at 7c.

A submersible pump 8 is mounted coaxially via strut 7d in the intake 7awhich is provided with a large-mesh grid 10 of a basket shape to prevententry of objects which may interfere with the pumping operation. Thepump 8 has a propeller-type 8a which drives the liquid in the directionof arrow 8b.

Downstream of the pump 8, 8a but upstream of the grid 6a, the duct 7 isprovided with guide plates 9 to reduce turbulence and maintainapproximately laminar flow of the liquid through the grid 6a. The latteris mounted by a vertical rib 6b upon the duct 7 and can be supplied withoxygen via the line 5 previously described. The vertical rib 6b can bemounted elastically at 6c and 6d upon the wall of the duct 7 and can beconnected to a vibrator 6e to produce oscillations of the ribstransverse to the direction of liquid flow as represented by the arrowe. The ribs 6 disperse the gas into the liquid as the latter flows inthe direction of arrow 8b through the device in the manner described inFIG. 1.

The assembly of FIG. 2 can be carried on a support, representeddiagrammatically at 7e enabling it to be rotated about a vertical axisor entrained in a circular path about a vertical axis in the clarifiertank in which it is disposed for aerating the sewage.

FIG. 3 shows, in diagrammatic cross section another embodiment of theinvention in which a vertically extending duct 11 is submerged in aclarifier tank and is provided with a plurality of vertically spacedhorizontal annular ribs 12 as described for the ribs 1 through 3previously. The ribs 12 are supported on vertical struts 12a suspendedfrom an outwardly extending flange 11a of the duct 11. A pipe 17,connected to an oxygen source, communicates with all of the ribs andinterconnects them to enable them to disperse in the liquid. The ribsare formed with the gas-permeable bodies 4 mentioned previously anddefine radially extending venturi gaps in the manner also describedabove.

A motor 16 has a shaft 15 carrying a rotor 15a which is formed with aplurality of angularly spaced struts 15b attaching a downwardlyconverging shell 15c to this shaft 15. On this shell 15c there are amultiplicity of vertical vanes 13 which form a radial pump forcing theliquid outwardly between the ribs 12. The liquid is drawn downwardlyover the top of the duct 11 as shown by the arrows in FIG. 3. Thisarrangement operates in the manner described with respect to FIG. 2except that the flow of liquid is radial with respect to the pump ratherthan axial.

In FIG. 4 we have shown an arrangement in which a vertical duct 25 isdisposed within the clarifier tank 26 and is open at its upper and lowerends therein. The upper end carries, via ribs 27, a motor 28 whose shaft29 is hollow and transmits oxygen from a distributor 30 to a pluralityof multiblade propellers 31 and 32 of aerodynamic configuration andprovided on their upper and lower surfaces with porous members 33 eachshown at 4 in FIG. 1.

The propeller blades are hollow and disperse the gas in the liquid aspreviously described. The blades cooperate with fixed vanes 34, also ofaerodynamic profile, and supplied with gas from the shaft 29 via lateralopenings therein. As each blade sweeps over a respective vane it definesa rearwardly diverging venturi passage therewith with the general effectdescribed in connection with FIGS. 1 and 2, the liquid being displacedgenerally through duct 25 as shown by the arrows.

FIGS. 5 and 6 show an embodiment in which the ribs 12 are connected tothe shell 11 which is here rotatably mounted on an outer sleeve 40 intowhich the liquid passes through its upper end submerged in the clarifiertank. The motor 16 is mounted on struts 41 of the sleeve 40 and hashollow shaft 42 communicating with an oxygen distributor 43 and openinginto a chamber 44 formed at the bottom of the rotor. The chamber 44communicates with aerodynamically shaped vertical members 45 whichfunction as radial vanes to displace the liquid outwardly, and inaddition are formed with gas-permeable bodies 46, corresponding to thebodies 4 described in connection with FIG. 1. The aerodynamically shapedvanes 45 diverge radially outwardly as can be seen from FIG. 6. Theshaft 42 can carry a gear 47 which meshes with a gear 48 on the strut41, the latter, in turn, meshing with a ring gear 49 on the interior ofthe duct 11. Consequently, the duct 11 and the ribs 12 are rotated inthe sense opposite the sense of rotation of members 45. The latter maycarry horizontal ribs as shown in FIG. 7, the latter being interfittedalternatingly with the ribs 12. The duct 11 is provided with adistributor 50 supplied with oxygen and communicating, e.g. a tube 17,with the ribs 12. Thus oxygen is fed into the gas by both sets ofcounterrotating ribs. The horizontal ribs of the inner rotor of thesystem of FIG. 7 is represented at 14. The ribs 14 are received betweenthe ribs 12 and, to allow these ribs to clear one another during theirrotations, the vanes 113 and 112a of the counterrotating rotors are setoff to opposite sides of the ribs 12 and 14.

We claim:
 1. A device for dispersing a gas in a liquid in the aerationof sewage in a clarifier tank, comprising a plurality of aerodynamicallyspaced ribs defining between them venturi passages, means for inducing aflow of liquid through said passages, said passages progressivelyconverging from an upstream side to a constricted portion and thereafterdiverging to a downstream side of the respective passage, andgas-permeable means along at least one surface of each of said ribsbounding a respective one of said passages in the region of therespective constriction for feeding gas to the liquid in a directionsubstantially perpendicular to the direction of liquid flow through therespective passage, a vertical duct in said tank open at its upper endand formed at its lower end with said ribs, said ribs being axiallyspaced horizontal rings, said means for displacing said liquid throughsaid passages including an axial intake, radial outflow pump having arotor surrounded by said rings for displacing liquid between them. 2.The device defined in claim 1 wherein said rotor is formed with hollowaerodynamically shaped ribs formed with gas-permeable surfaces, saiddevice further comprising means for supplying gas to said rotor.